1. Field of the Invention
This invention relates to semiconductor device fabrication, and more particularly, to the processing of so called chips of fragile semiconductor material in which complex densely packed circuits are embedded.
At the end of the processing line for semiconductor chips, it has become more or less standard practice to mount or position the chips on ceramic substrates or the like. However, in order to do so efficiently it becomes necessary to provide a suitable automated technique for moving or conveying the light-weight chips from their final stages of processing to a suitable loading point, thence to transport them quickly and efficiently to the mounting or packaging area.
What has been done conventionally in achieving the required rapid transport is to use a vibratory technique to induce movement of the chips. However, such vibratory transport method and like methods necessarily involve chip contact with the attendant possibilities of damage to the chips; hence, an ultimate decrease in yield of product.
As semiconductor or integrated circuit technologies continue to develop, with concentration on ever higher density circuits, this factor of damage to chips will become consequential. This is particularly so in the case of very large scale integrated circuit technologies which place great emphasis on improvement of overall yields. Necessarily in that case, it becomes an increasingly important goal to reduce manufacturing induced defects such as the aforenoted chip damage resulting from the conventional techniques adopted for transporting such chips.
Accordingly, the primary object of the present invention is to provide a means and technique for handling semiconductor chips very efficiently throughout the steps of the packaging phase of processing such that a minimum amount of contact between finished chips is involved in their automated transport.
Since one of the commonly produced integrated circuit chips includes in its finished state a group or plurality of contact pads, it is important that a system for handling such light-weight chips be capable of transporting them efficiently despite the unusual contour involved.
Accordingly, it is a more specific object of the present invention to provide a transport system that will efficiently convey such articles and provide such appropriate spacing between them that the aforenoted object of aluminum contact is fulfilled.
2. Background Art
For general teaching with respect to the conveying of slab shaped articles, reference may be made to U.S. Pat. No. 350,140. Further background material is provided by reference made in that patent to U.S. Pat. Nos. 2,805,898 and 3,180,688.
The basic object of the invention in U.S. Pat. No. 3,350,140 is to provide a system in which air consumption is reduced and the centralizing of articles in a conveying trough is achieved. To accomplish its objects, jets are provided in two rows parallel to the respective side walls and the jets in each row are inclined towards the other row at an angle causing amplification of the cushioned pressure. The system of that same patent also provides propulsion jets located along the center line of the trough.
Whatever merits the system of U.S. Pat. No. 3,350,140 possesses, it deals with the transport of articles much heavier than semiconductor chips, and which have a smooth underside; that is to say, there are no protrusions, mounds or other unusual contours that offer difficulty in the transport of the articles by the embodied technique.
As further background for the present invention, reference may be made to patents and articles which relate to transport systems for semiconductor wafers. Such systems for example are described in U.S. Pat. No. 4,081,201; U.S. Pat. No. 4,165,132; U.S. Pat. No. 3,976,330; IBM Technical Disclosure Bulletin Vol. 18, No. 7, December 1975 entitled "Self Centering Airlift Transport" by D. H. Apgar and T. C. Ku; and in IBM Journal of Research and Development, Vol. 23, July 1979 entitled "Air Film System for Handling Semiconductor Wafers" by J. A. Paivanas and J. K. Hassan. Another generalized device or system for supporting or conveying materials may be appreciated by reference to U.S. Pat. No. 2,678,237. Yet another systems that provide background for the present invention are those disclosed in U.S. Pat. No. 2,805,898 and U.S. Pat. No. 3,614,168.
Airtrack conveying systems such as that disclosed in the previously cited U.S. Pat. No. 3,976,330 are concerned principally with the need for self-centering in the conveying operation; however, they are not focused on problems connected with the transport of rectangular or prismatic parts, such as chips, which, particularly in the case of the provision of contact pads, have the further problem of an irregular surface due to the presence of solder mounds or the like. Moreover, the matter of obtaining spacing between parts is not a major objective in wafer conveyors and in fact, is not automatically achieved by differential air pressure, as is the case with the present invention. Also, systems for wafer transport, as contrasted with chip transport, often require special start controls, rather than the control being solely a function of track design and the shape of the transported part.